In recent years, an electronic key system (also called a smart entry system, etc.) is spread. In this electronic key system, ID authentication is performed by wireless communication between this system and a wireless electronic key (also called a portable device) carried by a user. Further, controls of locking/unlocking of a door lock, engine starting, etc. can be performed by commands from this portable device. In the above wireless electronic key, a demand for constructing this wireless electronic key as the card type wireless device made thin is raised to improve carrying convenience property by storing this wireless electronic key into a purse, etc. with a dramatic spread of an IC card, etc. as the background (3 mm or more and 5 mm or less in thickness).
The above electronic key system adopts a communication system able to execute a control operation such as the locking/unlocking of the door lock and the engine starting if the user approaches the automobile within a constant distance even when no user performs a special button operation, etc. with respect to the wireless electronic key. Concretely, a request radio wave sent out of the automobile side in one direction is received. ID authentication information, control command information relating to the above locking/unlocking or the engine starting, etc. are superposed on the transmitted radio wave and are sent out to the automobile side. In this case, when the user is distantly located, the wireless electronic key and the automobile do not react on communication. On the other hand, when the user approaches, there are many cases in which near distance type direct communication using a low frequency band (50 kHz or more and 500 kHz or less) is adopted so as to detect the radio wave by detouring the radio wave even when the user holds the wireless electronic key in any portion of the user's body.
The radio wave of the low frequency band has a very long wavelength. Therefore, in an antenna used for this radio wave, a so-called LF (Low Frequency) antenna provided by combining an antenna coil and a capacitor resonantly coupled to this antenna coil in a desirable frequency band is normally adopted. When the LF antenna is assembled into the card type wireless device, it is also necessary to reduce the thickness of this antenna coil in conformity with the thickness of a box body of the card type (e.g., 1 mm or more and 3 mm or less). In this case, it is desirable to mount the antenna coil onto a substrate in a shape for largely setting the aperture diameter of the antenna coil as much as possible to raise sensitivity with respect to the radio wave perpendicularly incident to the substrate face. It is effective to adopt the antenna coil with a core of high inductance so as to raise an antenna gain. However, a flat ferrite core is small in mechanical strength, and a crack, a fragment, etc. are easily caused by handling, etc. at a coil winding time. Accordingly, an air-core coil is normally adopted.
In the above-mentioned antenna coil, a demand for constructing this antenna coil as a surface mounting type discrete part is also raised from a viewpoint for improving productivity. Concretely, a coil main body is wound around a bobbin manufactured by resin, or the coil main body wound in outer setup is packaged in a case manufactured by resin to cope with such a demand. In the antenna coil formed as the discrete part in this way, a coil side terminal portion is positioned onto a substrate side pad through solder paste. Soldering processing is then performed by inserting this antenna coil into a reflow furnace and heating this antenna coil every substrate.
However, in the antenna coil mounted onto the substrate, the heating within the reflow furnace is not necessarily uniformly advanced and a temperature distribution is generated. Therefore, there is a case in which a warp is generated by its thermal stress. In this case, there are defects in that the coil side terminal portion is floated from the substrate side pad by this warp, and a soldering defect is easily caused.